The invention relates to a multiple-casing chimney of the kind described in claim 1. Such multiple-casing chimneys, or corresponding finished chimney parts, which are to be included in the inventions, are already known from DE-PS No. 19 22 389, for instance.
Due to different physical properties of the individual casings of the chimneys or of the finished parts of which they are constructed, dew points may be fallen below within the chimney which may result in soaking and tarring phenomena associated with a reduction of the heat insulating effect. These disadvantageous phenomena are further intensified by the aggressive smoke components carried along by the steam, particularly SO.sub.2 and SO.sub.3 and various hydrocarbons. Upon condensation, sulfurous or sulfuric acid may be precipitated, for example.
In the chimney type described, such effects are counteracted by a vapor barrier which is to prevent that moisture and aggressive components carried along get outside of the vapor barrier radially, instead being kept inside the radially inner core area of the chimney where temperatures do not yet fall below the dew point. But the measures required for this are rather costly as far as material and construction costs are concerned, and they are also susceptible to aging when many insulating materials are used.
It is an object of the invention to indicate an alternative solution to master the soaking or tarring phenomena mentioned, which solution is realizable with little technical expense and is less susceptible to ageing.